IBM PS/2 vs PC

The IBM PS/2 line was a fairly radical departure from the older IBM PC line. This was deliberate, as IBM wanted to disrupt the clone industry, which it saw as a threat to its business. Here’s a look back at the IBM PS/2 vs PC, the line it replaced.

IBM succeeded with the PC because it created an ecosystem, not just a PC. IBM’s misstep was creating an open architecture and then trying to close it back up after the fact with the PS/2. In IBM’s defense, it’s not clear whether they knew this at the time. If nothing else, in the case of the IBM PS/2 vs PC, IBM created a classic case study of open architecture vs closed.

One size fits all vs tailored

The IBM PC, in its standard early 1980s configuration
IBM built its original IBM PC, introduced in 1981, using mostly off-the-shelf parts.

One problem with the PC line was that it was one size fits all. Over time IBM released a few new models, but they still didn’t necessarily fit any individual’s particular need all that well. Each model had to fulfill a pretty wide array of needs. That was one reason the gray market existed.

It was wise for IBM to take this approach, however. In 1980, IBM didn’t really know what it was building. Small computers were still really new and IBM didn’t know how people would use them. So they built something extensible with expansion slots, similar to Apple’s approach with the Apple II.

From a collector’s standpoint it’s nice: The PC was a 4.77 MHz 8088 with floppy drives. The XT was a 4.77 MHz 8088 with a hard drive. The XT-286 was a 6 MHz 286 with a hard drive and an 8-bit bus. The AT was a 6 or 8 MHz 286 with a hard drive and a 16-bit bus. The need to tailor the solution is one reason you rarely find any IBM PC in factory stock configuration.

IBM PS/2 Model 30
This IBM PS/2 Model 30 featured an 8086 CPU and replaced the PC/XT in IBM’s product line.

The PS/2’s tailored approach

The PS/2, by contrast, had a different model for every CPU Intel offered, and frequently had both a compact model and a larger model. Sometimes that meant a compact desktop vs a bigger one, in the case of the Model 25 and 30, or a desktop vs a full tower, in the case of the Model 70 and 80.

If you just used a computer for typing letters and light spreadsheet use, an 8086-based Model 25 or 30 was fine. An accountant would more likely want a 286-based Model 50. The Model 60 made a good light-duty server. The Model 70 was an expensive computer for CAD and other similarly demanding work. The Model 80 was intended to be a powerful server.

The PS/2 business model was much closer to how computer makers do things today, although the models lasted much longer on the market than they do now.

Open architecture vs closed

PS/2 vs PC motherboard - PC/AT motherboard by Asus
This Asus P55T2P4 motherboard from the mid 1990s would fit in almost any PC or AT case, even one from the early 1980s.

The PC line was very open architecture. IBM published all of the specs for everything. Cloners simply re-implemented the specs, then could build nearly a bolt-for-bolt clone of IBM’s original. Many early clones were just that. Eventually they progressed to building stuff that looked different but still fit a particular layout, so a 386, 486, or even Pentium board would fit where a 286 board originally went.

It was entirely possible to take an early IBM PC, replace everything in the box, and end up with something that was all third party except for the case and badge. For most of the 1990s, I could walk into any computer store and buy an AT motherboard that would fit any AT case, IBM or non-IBM. I might neither know nor care who made the board.

Farewell to consistency

IBM closed it all up for the PS/2 line, except for the very basic Model 25 and Model 30, which retained the old ISA architecture. Anything faster, though, got the Microchannel (MCA) architecture. IBM would license it to other makers, but they paid for the privilege. Few took them up on it, and even fewer found it worthwhile to stick with it.

IBM PS/2 vs PC motherboard
This upgrade board, made by Reply, fit an IBM PS/2 Model 50 or 50Z. It looks nothing like an AT, ATX, or NLX board like you’d see in an ordinary PC. The slots that appear to be PCI slots are actually MCA slots.

Not only that, the motherboards tended to be different form factors between models. This was a compromise necessary to give more flexibility in the size of the computer. Not everyone wanted a big-footprint PC with 8 expansion slots. Most PS/2s took up a lot less desk space than a comparable PC.

A company named Reply offered upgrade boards for the most common PS/2 models. This allowed you to do things like stuff an Intel 486 DX4 into a Model 25 case. But that was expensive and the exception to the rule. Some businesses upgraded their PS/2 by swapping out motherboards. I knew people in college who had surplus PS/2s their dads’ employers had upgraded. But the PS/2 shop where I worked didn’t swap boards. At most, they’d drop in the occasional CPU upgrade.

You might occasionally find an IBM XT or AT case with a Pentium motherboard in it. The fastest upgrade you’ll find in a 1980s PS/2 is a 486, even though the PS/2 is a newer vintage.

Tool-less versus workbench

You could disassemble a PC with little more than a screwdriver. But there probably were a couple dozen screws in the case holding everything together. They weren’t all necessarily the same size either.

PS/2s were nicer to work on. You could disassemble a Model 50 or Model 70 without any tools at all. Everything snapped together for the most part.

In the 1990s, IBM went back from the PS/2 model to something closer to the industry standard PC model, only they used the NLX form factor rather than the AT or ATX form factor. Early in my career, I worked on PS/2s and the 1990s-generation IBM PCs. The PS/2s were a lot easier to work on.

A PC by any name is still a PC…

But in spite of the vast philosophical shift, the PS/2 was nothing more than a closed-architecture PC. It still had an x86 CPU inside, whether it was something Intel made or something IBM made to Intel specs. It still ran DOS. And it still ran Windows as long as the CPU supported the version of Windows you wanted to run. Not only that, in spite of the name, OS/2 didn’t just run on PS/2 machines. I ran OS/2 on a Compaq Presario PC for years.

Anything the PS/2 could do that a regular PC couldn’t ended up on a plug-in ISA board to give that capability to regular PCs. By far the most important one of those innovations was VGA graphics, which displaced the earlier CGA and EGA standards. The PS/2 mouse port was the second most important.

In 1987, IBM wanted the future to belong to the PS/2, but the rest of the industry collaborated to make sure that didn’t happen.

Collecting

Either line can be interesting to collect. The PC line had five variants of four models: the original 5150 PC, the 5160 PC/XT, the 5162 PC/XT 286, the 6 MHz 5170 PC/AT, and the 8 MHz 5170 PC/AT.

The PS/2 line was much more numerous, as the industry moved a lot faster in the late 1980s. You may want to choose an era and collect from it.

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